Peanut not only can effectively guarantee the safe supply of edible oil in China, but also is an important agricultural product with strong international competitiveness. With China's accession to the WTO, the domestic market is gradually opening to the international market, foreign agricultural products, such as wheat, corn and soybean, with high mechanization degree, large production scale and low production cost have poured in China, thereby impacting the domestic market. However, peanut still has great price advantages in the world, and has been on velvet in the international market. Its prices steadily rise, and its yield per mu in the same season is higher than other crops. Peanut contributes to developing water saving agriculture, improving soil fertility and protecting the agroecological environment. Developing peanut production is advantageous to the adjustment of agricultural planting structure, and is of significant importance for increasing farmers' income. How to improve peanut yield and quality to increase farmers' income is a problem to be solved by peanut researchers.
Scientific and rational balanced fertilization is one of the key factors to ensure the high yield of peanut. However, according to field investigation, generally there are a few misunderstandings on the fertilization process:
1. Peanut needs a small amount of fertilizer, and the amount of applied fertilizers does not greatly affect the yield.
2. Peanut can be fruited by spreading some urea on a rainy day without application of a base fertilizer.
3. If a large amount of fertilizers is applied, peanut tends to flourishingly grow, thereby wasting labor and material resources.
4. Fertilizers are applied aimlessly before knowing about what nutrients are required by peanut.
5. Fertilizers are spread in a stubble field in advance without centralized application.
18 elements are required for peanut growth, where nitrogen, phosphorus, potassium and calcium are most required, and sulfur, boron, molybdenum, zinc, manganese, iron and other trace elements are also indispensable. Through the growth period of peanut, the nutrient requirements are as follows: in the early stage, nitrogen fertilizer is mainly required, and application of proper amount of nitrogen fertilizer can promote peanut growth and root nodule formation in the seedling stage; in the intermediate stage, calcium fertilizer is mainly required, and is supplemented to contribute to ideotype formation and promote fruit plumpness; and in the later stage, nitrogen and potassium are mainly required, nitrogen fertilizer is supplemented to prevent later fertilizer deficiency, and potassium fertilizer promotes the transport of photosynthate to pod. Nitrogen fertilizer is volatile, phosphate fertilizer has weak ability to permeate upward and downward and migrate or diffuse leftward and rightward in soil, potassium fertilizer antagonizes calcium ions, and the root mass of peanut most actively assimilating nutrients is below the fruiting layer. Therefore, peanut fertilizer is most preferably applied into different layers or released by stages. At present, fertilizers are mainly applied by rationally arranging fertilizer application opportunities, types, quantity and method based on the principle of giving priority to base fertilizer, supplemented by top application, according to the characteristics of peanut's demand for fertilizer and based on the soil fertility. In order to achieve high yield, top application shall be arranged in the middle and later growth stages of peanut, but top application will affect pegging downward and growth. Some fertilizers shall be topdressed under strict conditions, thereby resulting in great difficulties in production. Therefore, top application is labor-consuming and time-consuming.
The prior art provides many solutions for this circumstance, and use of a controlled release fertilizer is one widely used solution thereof, such as a controlled release fertilizer for the flowering stage, a controlled release fertilizer for the growth stage, and a controlled release fertilizer for the fruiting stage. For example, CN105924294A discloses a granular controlled release fertilizer for peanut, the granules of which include three layers of controlled release films, namely, an outer layer controlled release film, an intermediate layer controlled release film and an inner layer controlled release film, wherein the outer side of the outer layer controlled release film is wrapped with a compound fertilizer in the seedling emergence stage, the space between the outer layer controlled release film and the intermediate layer controlled release film is filled with a compound fertilizer for the growth stage, the space between the intermediate layer controlled release film and the inner layer controlled release film is filled with a compound fertilizer for the flowering stage, and the inner layer controlled release film is wrapped with a compound fertilizer for the fruiting stage. The outer layer controlled release film can be degraded into a permeable film in 46 days, has an effective controlled release time of 25-35 days, and consists of the following raw materials in parts by weight: 2 parts of titanium dioxide, 1.5 parts of peat soil, 2 parts of clay, 1.2 parts of superfine delusterant powder wax, 5 parts of erucyl amide, 0.3 part of pentaerythrityl tetrastearate and 105 parts of polyethylene. The intermediate layer controlled release film can be degraded into a permeable film in 12 days, has an effective controlled release time of 47 days, and consists of the following raw materials in parts by weight: 1.6 parts of nanometer silicon dioxide powder, 1.2 parts of turfy soil, 2 parts of calcium carbonate powder, 1.2 parts of superfine delusterant powder wax, 5 parts of erucyl amide, 0.3 part of pentaerythrityl tetrastearate and 105 parts of polyethylene. The inner layer controlled release film can be degraded into a permeable film in 2.5-3.5 days, has an effective controlled release time of 815 days, and consists of the following raw materials in parts by weight: 1.2 parts of aluminium oxide, 2.2 parts of humus soil, 2 parts of calcium carbonate powder, 1.2 parts of superfine delusterant powder wax, 4 parts of erucyl amide, 0.3 part of pentaerythrityl tetrastearate and 115 parts of polyethylene. The controlled release fertilizer for peanut has the following disadvantages: firstly, its effective controlled release time range is 37-57 days, and it is mainly released before the pod-bearing stage without considering the fact that a lot of nutrients are required after the pod-bearing stage, especially in the fruit expansion stage; secondly, there is very little nitrogen in the outer layer, which cannot meet the growth needs in the seedling stage, and there is very little effective calcium in the intermediate layer, which cannot meet the pod growth needs; and thirdly, the release period of the active ingredients cannot very well meet the growth needs of peanut in various growth stages.
At present, there are many researches on controlled release fertilizers for peanut, but there are neither special controlled release fertilizers invented based on nutrient requirements of peanut in various growth stages, nor controlled release fertilizers integrating disease and pest control, chemical control, growth promotion, premature senescence prevention, and the like.